The invention relates to a label for an article, in particular for a reusable container, the backing material layer of the label being bondable onto the article by means of an adhesive layer and the label being removable from the article under the effect of heat, in particular in hot washing fluid or/and by thermal radiation. The articles may be beverage bottles or medicine bottles of glass or plastic, test tubes, repeatedly reusable outer packagings for a multiplicity of individual containers, in particular beverage bottle crates, etc.
For example, in the beverage industry, the containers used, for example bottles, are subject to a high quota of reuse. The containers are cleaned with each return before refilling, the labels also being detached during washing of the vessels. Then the vessels are refilled and relabelled corresponding to the beverage type filled. If the vessels are standardised for a particular product group, such as a beer bottle, the bottles returning to the brewery do not need to be resorted according to beer types, as would be the case with permanently predecorated bottles. The different labelling usually only occurs after filling. In the case of a direct printing of the bottle which cannot be washed off, large warehouse stocks of the appropriate predecorated bottles would have to be held in readiness.
In the beverage industry the washing of the vessels, i.e. the bottles, is generally carried out with a hot washing liquid, such as dilute caustic soda, heated to 60 to 90xc2x0 C., without additional mechanical support in the form of brushes, high-pressure nozzles etc.
Often, paper labels with wet-glue adhesive are used for the labelling of reusable containers. In this case, the wet-glue adhesive is applied to the full surface or in strips, the adhesive only being applied to the paper immediately before labelling. The disadvantage is that the filler must work with wet glue, that is to say contamination of the machine occurs and the handling of these labels is more difficult than that of self-adhesive labels.
This disadvantage is avoided by self-adhesive labels, which are obtained from the label suppliers already provided with adhesive. Because of the standardised washing-off conditions in the beverage industry, it was only possible to use paper-based labels until now. During washing off of the labels in the wash station, the water permeability of paper is exploited with the object that the wet-glue adhesive comes relatively quickly into full-surface contact with the washing liquid, and is completely detached in the predetermined washing timexe2x80x94of the order of some minutes, the adhesive however then usually going into solution in. the washing liquid. This high permeability for washing liquid and water is not possessed by the thermoplastic films used for many labelsxe2x80x94such as polyolefins, polycarbonates, polyesters, polyvinyl chlorides, polystyrenes, etc. Such films prevent the access of the washing liquid to the interface of the adhesive and container surface, so that the impermeable film labels can only be slowly detached from the label edge, which, without additional mechanical support, such as brushes, high-press nozzles, etc., does not permit complete removal of the labels within an economically justifiable time span. These mechanical means are undesirable because of the higher outlay.
In the case of a paper/wet-glue label, the adhesive swells and is then detached. In the case of paper labels precoated with adhesive, redispersible adhesives are also used. In addition, there are particular paper types that quickly disintegrate.
In particular in the beverage industry, however, there is an increasing demand for film-based labels precoated with adhesive. Such film labels, in contrast to paper labels, can be decorated in an extremely wide range of ways. In contrast to paper, they are also available in transparent form, have wet strength and can be dispensed onto the containers at high speed in standardised machines, without the need to work with adhesives, as for example in the case of the wet-glue paper label. Their mechanical properties such as tensile strength and extensibility are greatly superior to those of paper labels. However, it should also be possible to readily wash off such film labels with existing washing systems as easily as the paper labels often used until now.
In order, nevertheless, to be able to use film-based labels for reusable beverage bottles, label systems have now been developed, which permit complete removal of the labels after each return. In the so-called Contiroll system, the all-around labels are not full-surface adhesively bonded. Adhesive spots between the label and container surface are only provided in the region of the overlapping joint. To detach the label, the labels are slit in the axial direction of the container. In this process the container can easily be damaged. Furthermore, the slitting devices require high outlay. This system does not allow labelling over only a partial circumference of a bottle, since no continuous adhesive is present. Such all-round labels may be displaced on the container and foreign matter may penetrate between the label and the container surface, so that these labels do not come into consideration for so-called xe2x80x9cno-label lookxe2x80x9d applications, that is to say for applications in which, through the use of highly transparent film materials, the labels allow a view of the bottle or contents at the places where the label is unprinted.
Also known are so-called xe2x80x9csleeve labelsxe2x80x9d of shrinkable film. A film tube is slipped over the container and then shrunk on by the application of heat. Adhesive bonding between the label and container is entirely absent in this case. For removal, the label must in this case be elaborately slip open. A further disadvantage of these labels is that no enhanced decoration such as metallic effects or embossed sheet printing is possible, since these sleeves are printed directly from behind by reverse printing, and such enhanced decorations are not shrinkable to the same degree as the printed film substrate. In this case displacements and loss of brilliance would occur. Furthermore, both the last-mentioned labelling systems are material-intensive, since complete all-round decoration of the object is always necessary.
The object of the invention is therefore to provide a label of the type mentioned at the outset, which can be detached again from the article with little effort.
This object is achieved in that this label is characterised in that the backing material layer comprises a plastic film layer that is stretched in at least one direction and shrinks back under the effect of heat, for example the temperature of the washing fluid or/and by thermal radiation, so as to overcome the retention force of the adhesive layer.
By virtue of the effect of heat, shrinking back of the plastic film occurs, while at the same time the adhesive loses adhesive force. By this means, the label detaches gradually from the article, for example from the edge or with the formation of channels, and can be easily removed within an extremely short time.
The hot washing fluid by be in the form of a liquid, gas or vapour, or a mixture thereof and contain surfactants and lyes, in particular caustic soda. In the case of thermal radiation, infrared radiators or else other radiators with an infrared component may be used. The labels are detached particularly quickly under the combined effect of hot washing liquid and thermal radiation.
If a washing liquid is used as washing fluid, it can penetrate to the adhesive even faster from the edge or through the channels, and detach the adhesive in an extremely short time. The adhesive may be such that it is not substantially detached under the effect of pure water, however detaches relatively quickly from the container under the effect of the washing liquid, for example 1-2% hot caustic soda, which is conventionally used in the beverage industry.
Preferably the shrinking force of the film layer and the bonding effect of the adhesive are matched to one another such that the label can be completely detached from the container at a temperature of more than 50xc2x0 C., in particular more than 60xc2x0 C., over a duration of 10 sec. to 15 min., in particular 3 to 6 min., under the effect of the washing liquid. These are typical washing conditions in conventional bottle washing systems in the beverage industry.
Preferably the decrease of the bonding effect of the adhesive is based on a decrease of its viscosity with the heating of the label during the washing process.
Preferably the retention force of the adhesive towards the label is chosen higher than the release force effected by shrinkage of the plastic film layer, so that with detachment of the label from the article the adhesive layer remains on the label and can be removed from the washing liquid and disposed of together with the label, for example by means of a simple sieve. By this procedure it is also achieved that adhesive cannot accumulate in the washing liquid.
The adhesive is preferably one that does not dissolve in water, at least until detachment of the label, in particular a redispersible adhesive such as a dispersion adhesive based on acrylate or copolymeric acrylate/polyurethane compounds and copolymers with an acrylate proportion (e.g. rubber/acrylate).
Preferably the adhesive is applied to the label material covering the full surface or in regions with gaps, if appropriate in patterns. The full-surface application permits a design as a so-called xe2x80x9cno-label lookxe2x80x9d label, which, at places where it is unprinted, allows a view through to the product. In the case of adhesives applied in regions, i.e. in a shaped manner, the appearance is usually disturbed.
The adhesive layer may also be a hot-melt adhesive or a glue or a radiation-curing or thermally melting adhesive applied to the article or to the label immediately before labelling.
Preferably the label serves for adhesion to a cylindrically curved surface of the article, such as a beverage bottle, its stretching direction orxe2x80x94in the case of biaxially stretched film materialxe2x80x94its main stretching direction extending in the circumferential direction of the container or transverse to, in particular perpendicular to, the circumferential direction of the container. In the case of plastic films, it may be a single monoaxially or biaxially stretched plastic film layer, or a plurality of plastic film layers whose respective stretching directions or main stretching directions are often essentially identical. In this case the plurality of plastic film layers may be coextruded or manufactured individually and bonded to one another by means of lamination adhesive. Both film layers may be shrinkably stretched in the same direction or in crossing directions to the same or different extents, the more weakly shrinking film layer in the label laminate coming preferably to lie at the bottom, that is to say at the side facing the adhesive layer. The two film layers can be bonded to one another by means of lamination adhesive.
Furthermore, it is possible to use a shrinkably stretched film for only one of these film layers, in particular the lowermost film layer, and for the others to use a non-shrinking film, i.e. a thermally fixed, dimensionally stable film. In this case, the two film layers can also be bonded to one another by means of lamination adhesive, i.e. a one or two-component lamination adhesive such as a polyurethane-based adhesive, and pressure-sensitive adhesives or else thermally activatable adhesives.
It is possible that the (main) stretching direction and therefore the (main) back-shrinking direction of the plastic film(s) extends in the circumferential direction of the cylindrical container, so that shortly before the complete detachment the label only adheres to the container in the vicinity of a line. Another possibility consists in arranging the (main) stretching direction of the plastic film(s) transversely to the circumferential direction of the container, so that, shortly before complete detachment, the label only adheres to the container in the vicinity of a point.
Preferably the degree of shrinkage of at least one plastic film layerxe2x80x94at least in the main shrinkage directionxe2x80x94under heating to one of the above-mentioned temperatures is in the region of xe2x89xa75%, in particular xe2x89xa710%, more particularly xe2x89xa715-20% or more.
The plastic film layer is preferably made from monoaxially or biaxially stretched polyethylene terephthalate (PET) film or polyvinyl chloride (PVC) film, which shows a high degree of shrinkage.
To ensure that during and after washing off, the adhesive remains bonded to the label and can be easily disposed of, the label layer bearing the adhesive can be treated before application of the adhesive bonding agent, for example by corona treatment, flame pretreatment, plasma pretreatment or chemical grafting or with the aid of an adhesion-promoting intermediate layer containing, for example, chlorinated polyolefins, chlorinated rubber, ethylene/vinyl acetate (EVA) copolymer, chlorinated polypropylene or polymerised ethylene/acrylamide comonomers.
The label according to the invention can have the above-mentioned advantages over conventional paper labels and at the same time fulfil three main requirements:
1. The label can be washed off in conventional industrial washing systems
2. The washing liquid accumulates neither adhesive nor film components, since these can be filtered out in an extremely simple manner by means of a sieve.
3. The film label can be detached from the article as an entirety together with the adhesive bonding thereto, leaving no residues.